By Paul Danzer, N1II Open Wire Feed Line— A Second Look Put up the longest dipole you can fit, feed it with open wire line, connect it to the balanced output of your tuner and—poof! Instant multiband . Is life really that simple?

he answer is yes…this actually transmission lines will show an increased weight, small-sized . works. But there are a few things loss when the SWR is not 1:1, and in this But with the same 1000 Ω resistive and Tthat should be considered before case the additional loss was again only 1000 Ω inductive imaginary load, the you dump that G5RV, cut down all your 0.270 dB—small enough to be ignored. additional transmission line loss TLA tells other antennas and replace them with just This was not true with coax…in this us is 6.797 dB. Wow—too much already! one dipole. A few practical consider- case 75 Ω, RG-59/U, and a perfect 75 Ω That is why open wire line has been ations may change the way you build, dipole. At 28 MHz the loss was about suggested many times for a multiband tune or use a single, multiband dipole. 2.01 dB. That’s noticeable, but perhaps dipole. With a mismatch, the increased Open wire line has a very large advan- acceptable if you chose to use a light- line loss does not amount to very much. tage. By open wire line, we mean both commercial ladder line as well as two par- allel wires with plastic or ceramic insu- lating bars. The TLA program, included on a disk with the 17th through the 19th editions of The ARRL Antenna Book1 gives us a way to see the primary advan- tage of open wire line quickly and di- rectly. (The 20th edition has a newer program, TLW for Windows.) This program lets us pick a transmis- sion line and impedances (and therefore the SWR on the line) and presents us with the losses on the line. The few numbers given here will be sufficient for an un- derstanding of what’s going on, even if Figure 1—A few hours in the wind and you are no longer connected. you aren’t mathematically inclined. Open Wire Versus Coax Using TLA, four sets of calculations were run. Each was for 100 feet of trans- mission line at 28 MHz. Ladder line, the 450 Ω variety, was connected to an imagi- nary perfectly matched antenna of some sort. The total transmission line loss was 0.201 dB, so small as to be silly. (A 3 dB loss would mean you have lost half of your power.) But, since we are interested in multiband operation, on other bands the antenna will be mismatched. In order to use nice, round numbers, a new antenna was imagined that looked like 1000 Ω resistive and 1000 Ω inductive. All

1Notes appear on page 36. Figure 2—The TLA program output reveals losses and voltages. 34 April 2004

DanzerNEW.pmd 34 2/20/2004, 7:38 AM Figure 3—The A solution shows the conventional approach, and B the high-efficiency, practical approach. Figure 4—This tuner design predates , but is still practical for today.

A 100 Foot Test Dipole To see what the results with a real antenna would be, a 100 foot long dipole, 40 feet in the air, was analyzed using EZNEC (to find its input impedance) and TLA (to find the transmission line losses and voltages). When fed with 600 Ω open-wire line, the dipole, as expected, was a reasonable choice for all bands except 160 meters, and perhaps a bit questionable for 80 meters.

Total Loss, Including that Additional Loss Frequency Complex Impedance Voltage due to SWR due to SWR Alone SWR at Input Ω Ω (MHz) Zin ( ) (V) (dB) (dB) of 600 Line 1.82 3.5963 –j1694.1 3700 7.66 7.64 39.71 3.6 20.156 – j466.45 1550 0.769 0.737 7.13 7.1 413.41 + j1155.7 650 0.154 0.107 9.15 10.1 2551.4 – j2804.4 750 0.259 0.202 9.15 14.1 106.41 – j181.65 600 0.221 0.152 5.90 18.1 1168 + j1674 600 0.249 0.170 5.97 21.1 567.29 – j1630.7 750 0.424 0.338 8.85 24.9 144.27 + j151.09 500 0.212 0.117 4.25 28.1 1498.1 + j1610.1 550 0.276 0.175 5.27

As you can see, the total loss for this feed line was less than 1 dB for all bands, except 160 meters. With 100 W delivered to the feed line, the voltage seen (only the peak value is shown here) is a bit high on 80 meters, but it goes out of sight on 160. As expected, with open-wire feed line, the additional losses due to SWR remain remarkably low for SWR values up to 9:1. Only on 160, where the SWR climbs to almost 40:1, do the additional losses due to SWR become important. Don’t let numbers like j1630.7 and 3.5963 throw you. The number of significant figures shown here are artifacts of the com- puter calculation, and the actual accuracy is nowhere as precise as shown. If you use another simulation program, or make other assumptions, you own figures may vary from this table by 20% or more.

There are, however, a few problems with lem. Almost 1700 Vrms is floating around. anced open wire transmission system is a this approach. This voltage jumps, in the practical case, very simple solution, but it does not take when you try to feed a short dipole, such into account the . Problem #1: Mechanical as one cut for 80 meters, on a lower fre- Strangely enough, the balun problem Before you even start, consider how quency band, such as 160 meters. Keep has been known “forever,” and until only you are going to connect the open-wire your fire extinguisher handy! recently it has been ignored. In the 10th line to the dipole. Ladder line is not much edition (1964) of The ARRL Antenna Book, of a problem; there are commercial con- Problem #3: Work, But Only the following was printed on this topic: nectors available. For most other lines, Sometimes The principles on which balun coils you will have to fabricate a clamp. If you Most commercial and homebrew tun- operate should make it obvious that the can imagine soldering the line to the di- ers consist of a T or other configuration s.w.r. on the transmission line to the an- pole, as shown in Figure 1, also imagine that is essentially an unbalanced input to tenna must be close to 1 to 1. If it is not, the input impedance of each bifilar wind- the line breaking off after few months of unbalanced output. Simple and straight- ing will depend on its electrical charac- flexing in the wind. It’s a problem you forward. teristics and the input impedance of the should be aware of.2 Many years ago, in school, I was taught main transmission line…and the transfor- an interesting concept: “For every com- mation ratio likewise will vary over wide Problem #2: How Damp is My plex problem, there is invariably a very limits. Shack? simple solution and invariably that simple Translated, this means that if the balun The TLA program output for mis- solution is absolutely wrong!”3 Taking the is not operated under matched conditions, matched 450 Ω line is shown in Figure 2. unbalanced (coax) output of a rig, putting it does not operate as the simple unbal- The fourth line from the bottom of the it through a tuner, and then to a balun to anced to balun device you might imag- screen print is an indicator of another prob- take advantage of the low loss of a bal- ine. Moreover, from a practical point of

April 2004 35

DanzerNEW.pmd 35 2/20/2004, 7:39 AM view, the balun core will get hot. This could be fixed and adjusted with a small at Housatonic Community College in Connecti- means that some of the power you variable capacitor as shown, or it could cut. When he was on the ARRL HQ staff, thought you were sending to the antenna actually be moved mechanically in and Paul wrote and edited ARRL books. He is is actually going to raise the temperature out of the main inductor to achieve a also an ARRL Technical Advisor. He can be of your tuner and your shack. There are match. reached at 2 Dawn Rd, Norwalk, CT 06851; easier ways to heat the room! [email protected]. Open Wire Lines—Not a Bad Idea What are the Solutions? As long as your open wire feed sys- Figure 3 shows one neat and perhaps tem is really matched, and the balun NEW BOOKS elegant solution. The normal, but not de- is used under reasonable SWR condi- sirable approach is shown in Figure 3A. tions, open wire does allow you to TIPS TO THE TOP FROM DX PROS But, if you reverse the flow, and put the use one dipole on many bands with rea- š The new book Tips To The Top From DX balun first, then the tuner can operate as sonable transmission line efficiency. Pros describes dozens of DX success fac- 50 Ω in and whatever is needed out, while Unfortunately, it is not as simple as con- tors and operating tips collected in a sur- the balun stays as 1:1. necting the line to the two terminals vey of 100 outstanding DXers. Written by This is the approach shown in Figure marked “balanced” on the back of your Devere “Dee” Logan, W1HEO, a veteran DXer and DXCC 3B. A practical, elegant high power tuner tuner. But with a little care, one dipole Honor Roll mem- with this configuration designed by Dean will serve all. ber, the 32-page Straw, N6BV, was included in the 1998 book contains de- Notes through 2002 editions of The ARRL 1 tails of a survey 4 Available from your local dealer or the ARRL Handbook for Radio Amateurs. It was Bookstore. Order no. 9043. Telephone toll- of leading DX op- put together to squeeze every last watt free in the US 888-277-5289 or 860-594- erators listed in out of the tuner. Any reasonable tuner, 0355, fax 860-594-0303; www.arrl.org/ the DXCC Honor shop/; [email protected]. Roll, Worked All however, mounted on insulators, within 2 One solution to the breakage problem is to Zones and CQ a second enclosure, can be used in this strain relieve the ladder line by passing the DX rankings, plus mode. Each knob shaft would have to be conductors through the holes first and then looping and soldering them to the a number of key extended with an insulated section, and antenna wires. This has worked for the edi- DXpedit-ioners. a good quality 1:1 unbalanced to balanced tor for many years.—Ed. The 10 chapters balun used between the rig and tuner. 3Attributable to H. L. Mencken: “…there is al- include sugges- A second solution dates back to the ways a well-known solution to every human tions for equip- problem—neat, plausible, and wrong.”—Ed. ment, antennas, pileup strategies, locating 1930s, and is shown in Figure 4. The 4It is also included in the current (20th edition) small winding is called a “link,” and the the DX, getting the QSL, tips for reaching of The ARRL Antenna Book on p 25-15. the top and more. Tips To The Top From configuration is referred to as “link DX Pros is available for $9 plus $1.50 ship- coupled.” The unbalanced input for the Paul Danzer, N1II, has been a licensed ham ping and handling (check or money order rig goes to the link, and the balanced for over 50 years. Paul has both Bachelor’s only—payable to D.E. Logan) from D.E. transmission lines tapped off symmetri- and Master’s degrees in EE, and after many Logan Public Relations, 9901 Cypress cally from the tuned circuit. The link years as an electronic engineer, he now teaches Circle, Mentor, OH 44060.

STRAYS

BYRON LICHTENWALNER, W3WKR LARRY ROBBINS, W3CEI

SKN aficionado: When Larry Robbins, W3CEI, of Middletown, Pennsylvania, sent us this photo of his straight key collection (and Heath SB-313 receiver and Knight T150A ), he Byron Lichtenwalner, W3WKR, of Stroudsburg, Pennsylvania, included a note that said, “I am looking forward to a 24 hour searches the bands from this impressive station. It features an swing cycle of brass type music, hand-crafted with care and ICOM IC-765, PK900 TNC, Alpha amplifier, IBM PC running skill.” The results of the 2004 running of Straight Key Night Writelog and a Mosley PRO-57B at 65 feet on a crankup tower. appear on page 110 of this issue. 36 April 2004

DanzerNEW.pmd 36 2/20/2004, 7:44 AM